An axial gas turbine comprises a compressor, a combustion chamber and a turbine part. In the compressor, combustion air is highly compressed, and this highly compressed combustion air is then burnt with fuel in the combustion chamber. The hot gas which is formed is passed through a hot-gas duct in the turbine part. Guide vane rings and rotor blade rings follow one another alternately in the turbine part. Guide vanes and rotor blades are arranged adjacent to one another in the circumferential direction in each of these blade/vane rings.
The temperatures in a gas turbine of this type may reach levels which exceed the melting points of the materials that can be used and/or reduce the hot strength of the materials to an unacceptable extent. For this reason, the components in the hot-gas duct are often cooled with a cooling medium. For this purpose air is generally branched off from the compressor to act as cooling air. The demand for cooling drops along the direction of flow in the hot-gas duct. For this reason, cooling air at a lower pressure level than cooling air for front turbine stages is sufficient to cool rear turbine stages. To minimize the consumption of cooling air, since it reduces the efficiency of the gas turbine, the axially different turbine stages, i.e. the different blade/vane rings, are acted on by cooling air from different pressure levels. Blade/vane rings which lie further forward in the direction of flow are supplied with compressed air at a higher pressure than blade/vane rings lying further to the rear in the direction of flow.
In view of this different supply of cooling air even to blade/vane rings positioned next to one another, it is necessary to form a seal between the different pressure levels. A seal is also required in order to prevent hot gas from being mixed into the cooling air and therefore to prevent a reduced cooling action.
U.S. Pat. No. 5,833,244 shows a gas turbine sealing arrangement. The sealing of two adjacent blade/vane rings is in this case achieved by a labyrinth sealing system. Individual sealing elements are arranged in grooves of rotor disks. These sealing segments have tooth-like elevations which run transversely to the direction of flow, are arranged in succession in the axial direction and are arranged opposite a guide vane tip. Arranging these segments next to one another in the circumferential direction provides a labyrinth sealing system which runs all the way around the circumferential direction and is in particular also suitable for sealing in large gas turbines.
The sealing system located between two blade/vane rings in the axial direction is distinct from a sealing arrangement which acts in the circumferential direction between blades/vanes of a single blade/vane ring. A circumferential seal of the latter type is used to shield the hot gas flowing in the hot-gas duct from the rotor discs or guide vane carriers. Arrangements of this type are disclosed, for example, in U.S. Pat. No. 5,785,499 or U.S. Pat. No. 6,273,683.